Hydrocarbons may be recovered from hydrocarbon containing formations by penetrating the formation with one or more wells. Hydrocarbons may flow to the surface through the wells. Conditions (e.g., permeability, hydrocarbon concentration, porosity, temperature, pressure) of the hydrocarbon containing formation may affect the economic viability of hydrocarbon production from the hydrocarbon containing formation. A hydrocarbon containing formation may have natural energy (e.g., gas, water) to aid in mobilizing hydrocarbons to the surface of the hydrocarbon containing formation. Natural energy may be in the form of water. Water may exert pressure to mobilize hydrocarbons to one or more production wells. Gas may be present in the hydrocarbon containing formation (reservoir) at sufficient pressures to mobilize hydrocarbons to one or more production wells. The natural energy source may become depleted over time. Supplemental recovery processes may be used to continue recovery of hydrocarbons from the hydrocarbon containing formation. Examples of supplemental processes include waterflooding, polymer flooding, alkali flooding, thermal processes, solution flooding or combinations thereof.
In chemical Enhanced Oil Recovery (EOR) the mobilization of residual oil saturation is achieved through surfactants which generate a sufficiently (ultra) low crude oil/water interfacial tension (IFT) to give a capillary number large enough to overcome capillary forces and allow the oil to flow (I. Chatzis and N. R. Morrows, “Correlation of capillary number relationship for sandstone”. SPE Journal, Vol 29, pp 555-562, 1989). However, reservoirs have different characteristics (crude oil type, temperature and the water composition—salinity, hardness) and it is desirable that the structures of added surfactant(s) be matched to these conditions to achieve a low IFT. In addition, a promising surfactant must fulfill other important criteria including low rock retention, compatibility with polymer, thermal and hydrolytic stability and acceptable cost.
Compositions and methods for enhanced hydrocarbons recovery utilizing an alpha olefin sulfate-containing surfactant component are known. U.S. Pat. Nos. 4,488,976 and 4,537,253 describe enhanced oil or recovery compositions containing such a component. Compositions and methods for enhanced hydrocarbons recovery utilizing internal olefin sulfonates are also known. Such a surfactant composition is described in U.S. Pat. No. 4,597,879. The compositions described in the foregoing patents have the disadvantages that brine solubility and divalent ion tolerance are insufficient at certain reservoir conditions. Furthermore, it would be advantageous if the IFT which can be achieved in relatively severe salinity and hardness conditions could be improved.
As the carbon chain length of internal olefin sulfonates is increased, the solubility of the of internal olefin sulfonates in saline and reservoir brine solutions can be difficult, particularly at higher salinities. The aqueous injection solution should be single phase with no signs of precipitation at ambient temperature to be a viable fluid for injection in a reservoir. The approach traditionally used to aid solubility has been the use of co-solvents such as sec-butanol and isopropanol. In general, the concentration of the cosurfactants or cosolvents must be greater than about 1 wt % in order to maintain the solubility of the internal olefin sulfonate in high salinity brine.
U.S. Pat. No. 5,068,043 describes a petroleum acid soap-containing surfactant system for waterflooding wherein a cosurfactant comprising a C17-20 or a C20-24 internal olefin sulfonate was used. In “Field Test of Cosurfactant-enhanced Alkaline Flooding” by Falls et al., Society of Petroleum Engineers Reservoir Engineering, 1994, the authors describe the use of about 0.06 wt % NEODOL® 25-12 surfactant in a C17-20 or a C20-24 internal olefin sulfonate waterflooding composition to keep the composition as a single phase at ambient temperature without affecting performance at reservoir temperature significantly. The water had a salinity of about 0.4 wt % sodium chloride. NEODOL® 25-12 is an ethoxylated C12-15 alcohol containing about 12 moles of ethylene oxide per mole of alcohol. These materials, used individually, also have disadvantages under relatively severe conditions of salinity and hardness.